M. J. Santos

Using ultrasound backscattering signals and Nakagami statistical distribution to assess regional cataract hardness.

This study aims to analyze the protein aggregates spatial distribution for different cataract degrees, and correlate this information with the lens acoustical parameters and by this way, assess the cataract regional hardness. Different cataract degrees were induced ex vivo in porcine lenses. A 25 MHz ultrasonic transducer was used to obtain the acoustical parameters (velocity, attenuation, and backscattering signals). B-scan and Nakagami images were constructed. Also, lenses with different cataract degrees were sliced in two regions (nucleus and cortex), for fibers and collagen detection. A significant increase with cataract formation was found for the velocity, attenuation, and brightness intensity of the B-scan images and Nakagami m parameter (p <; 0.01). The acoustical parameters showed a good to moderate correlation with the m parameter for the different stages of cataract formation. A strong correlation was found between the protein aggregates in the cortex and the m parameter. Lenses without cataract are characterized using a classification and regression tree, by a mean brightness intensity ≤0.351, a variance of the B-scan brightness intensity ≤0.070, a velocity ≤1625 m/s, and an attenuation ≤0.415 dB/mm·MHz (sensitivity: 100% and specificity: 72.6%). To characterize different cataract degrees, the m parameter should be considered. Initial stages of cataract are characterized by a mean brightness intensity >0.351 and a variance of the m parameter >0.110. Advanced stages of cataract are characterized by a mean brightness intensity >0.351, a variance of the m parameter ≤0.110, and a mean m parameter >0.374. For initial and advanced stages of cataract, a sensitivity of 78.4% and a specificity of 86.5% are obtained.

Fatigue performance of Kevlar/epoxy composites with filled matrix by cork powder

The objective of this study is to characterize the fatigue strength of a Kevlar/epoxy laminate composite as well as the benefits obtained by using an epoxy matrix filled by cork powder. Twelve ply laminates, all in the same direction, of woven bi-directional Kevlar 292, were prepared by hand lay-up, using an SR 1500 epoxy resin. The composite sheets were produced by a vacuum moulding process. The addition of cork powder reduces the static strength, however, in terms of fatigue strength a similar behavior was found for both laminates.

Ultrasonic Guided Waves Scattering Effects From Defects in Adhesively Bonded Lap Joints Using Pitch and Catch and Pulse-Echo Techniques

In this article a method to evaluate defect dimensions in adhesively bonded lap joints based on the measurement of scattering effects of ultrasonic guided waves is presented. A simplified theoretical model is proposed which was initially tested in plates with through holes. The experimental results obtained using both pitch-and-catch and pulse-echo techniques for 500 kHz and 1 MHz frequencies confirm the validity of this model. To evaluate the lap joint defects, a set of samples with artificial defects were manufactured and the form and dimensions were confirmed using C-scan ultrasonic images. With the same methodology used in through-hole analysis, scattering effects of defects were measured. The results obtained with the pitch-and-catch technique with 1 MHz transducers allow us to say that an estimate of defect dimensions could be done by using the proposed model with reasonable accuracy and according with the predictions.

Imaging Particulate Two-Phase Flow in Liquid Suspensions with Electric Impedance Tomography

Different approaches have been followed to model the hydraulic transport of particles, ranging from pure empirical correlations to general models based on fundamental principles. However, these models suffer from uncertainties associated with the parameters in the constitutive equations and scarcity of experimental data in the literature. Nonintrusive techniques such as electric impedance tomography (EIT) can be used to circumvent the difficulties associated with sampling techniques. EIT is an imaging technique for the phase distribution in a two-phase flow field, allowing reconstructing the resistivity/conductivity distribution gradients from electrical data in a medium subjected to arbitrary excitations. Our best efforts were concentrated on the development of a new EIT system that is analogue based, portable, low-cost, and capable of providing high-quality sharp images when used to characterize the flow of particle suspensions. A voltage source was used, rather than a more complex and costly current source, since it provided the EIT system with a more precise and flexible current output. The data acquisition system consists of 16 electrodes equally spaced in the boundary of a tube and a custom dedicated electronic apparatus. The software supplies results in the form of two-dimensional reconstructed images that allow mapping the phase distribution inside the tube.

Lamb Waves Technique Applied to the Characterization of Defects in Friction Stir Welding of Aluminum Plates: Comparison with X-Ray and Ultrasonic C-Scan

Friction stir welding presents several advantages when compared with conventional arc welding processes, mainly in the welding of aluminum alloys. However, this welding technology leads to some degradation in the mechanical properties of welds, namely defect formation, which demands suitable nondestructive testing methods. The most common defects are mainly cold laps and voids, as a result of the large plastic deformation and hardening of the material as well as its complex flow behavior. In particular, the void appearance frequency may be correlated with the weld travel speed, though other welding parameters may contribute to the phenomenon. The purpose of this paper is to characterize such defects using conventional x-rays and ultrasonic C-scan, and a new method based on ultrasonic guided waves. The proposed new method presents as an attractive solution when large structures need to be inspected since propagation over long distances from a single probe position is possible with low attenuation. Additional characteristics such as straightforward inspection and testing fastness make the technique very cost effective. Test samples were fabricated using aluminum alloys of 3 mm in thickness, with different travel speeds and overlapping welds. This welding procedure gave rise to different defect sizes. Experimental results using both conventional and ultrasonic guided waves methods have confirmed the presence of the defects.

In-Vivo Automatic Nuclear Cataract Detection and Classification in an Animal Model by Ultrasounds

Objective: To early detect nuclear cataract in vivo and automatically classify its severity degree, based on the ultrasound technique, using machine learning. Methods: A 20-MHz ophthalmic ultrasound probe with a focal length of 8.9 mm and an active diameter of 3 mm was used. Twenty-seven features in time and frequency domain were extracted for cataract detection and classification with support vector machine (SVM), Bayes, multilayer perceptron, and random forest classifiers. Fifty rats were used: 14 as control and 36 as study group. An animal model for nuclear cataract was developed. Twelve rats with incipient, 13 with moderate, and 11 with severe cataract were obtained. The hardness of the nucleus and the cortex regions was objectively measured in 12 rats using the NanoTest. Results: Velocity, attenuation, and frequency downshift significantly increased with cataract formation (P <; 0.001). The SVM classifier showed the higher performance for the automatic classification of cataract severity, with a precision, sensitivity, and specificity of 99.7% (relative absolute error of 0.4%). A statistically significant difference was found for the hardness of the different cataract degrees (P = 0.016). The nucleus showed a higher hardness increase with cataract formation (P = 0.049). A moderate-to-good correlation between the features and the nucleus hardness was found in 23 out of the 27 features. Conclusion: The developed methodology made possible detecting the nuclear cataract in-vivo in early stages, classifying automatically its severity degree and estimating its hardness. Significance: Based on this work, a medical prototype will be developed for early cataract detection, classification, and hardness estimation.

New approach for objective cataract classification based on ultrasound techniques using multiclass SVM classifiers

In the present work, ultrasound A-scan signals were acquired from healthy and cataractous porcine lenses. B-mode images were reconstructed from the collected signals. The parametric Nakagami images were subsequently constructed from the B-mode images. Acoustical and spectral parameters were obtained from the central region of the lens. Image textural parameters were extracted from the B-scan and Nakagami images. Ninety-seven parameters were extracted from a total of 75 healthy and 135 cataractous lenses. Lenses with cataract were split in two groups: incipient and advanced cataract, corresponding to a 60 and 120 minutes of immersion time in a cataract induction solution, respectively. The obtained parameters were subjected to feature selection with Principal Component Analysis (PCA) and used for classification through a multiclass Support Vector Machine (SVM). This paper shows that multiclass SVM can perform effectively the classification of the cataract severity, with an overall performance of 89%, classifying correctly 93% of the features.

Characterization of scatterers concentration in cataractous lens using Nakagami distribution by ultrasounds

Cataract affects more than 20 million people in the world. Its formation is associated with the increase of protein aggregation in the eye lens. In the early stages the protein aggregates act as light scatterers and in the advanced stages these aggregates increase in size preventing the light propagation through the eye. This work aims to analyze the protein aggregates and its spatial distribution, for different stages of cataract formation. Cataract was induced in porcine lenses by immersion in an ethanol:2-propanol:formalin solution. Slices of 50 μm in thickness were obtained from the nucleus and the cortex, to locally analyze the frequency dependent attenuation and the Nakagami m parameter. The slices were stained and imaged with an inverted microscope. With cataract formation a significant increase was found for the ultrasound velocity (p>0.001), the frequency dependent attenuation (p<;0.001), the backscattering signals intensity - B-Scan images and the Nakagami m parameter (p<;0.001). The increase of the Nakagami m parameter in the cortex was in agreement with the increasing of the protein aggregates observed in the slices in this region, for different stages of cataract formation. The same was not observed for the nucleus, due to the higher compaction of the fibers in the nucleus in the advanced stages of the cataract, leading to weak backscattering signals. The results suggest that the interpretation of backscattering signals by the Nakagami distribution, when combined with the knowledge of the physical scatter properties are challenging for obtaining a distribution map of cataract hardness by a noninvasive method.

Using of the ultrasound frequency dependent attenuation and Nakagami distribution for cataract evaluation

Cataract is a clouding or opacity of the normally transparent crystalline lens of the eye. The cataract formation is associated with the increase of both inner fiber compaction and protein aggregation, which can be characterized by ultrasound backscattering. In this study, the tissue scatterers changing with cataract formation was investigated, and their influence in the frequency dependent attenuation such as in the Nakagami distribution was analyzed. For this purpose, cataracts were induced in twenty porcine lenses. A 25 MHz focused transducer was used to estimate the ultrasound attenuation considering the spectral ratio between echo signals from a reflector with and without lenses inserted. A power-law frequency dependence model was used to study the frequency dependent attenuation. The analyzed signals showed high backscattering and also a variation of the Nakagami parameter with cataract formation, indicating a scatter size increase. This conclusion could be important to assess the cataract hardness and to provide the correct information about its type and severity.

Ultrasound techniques for lens hardness characterization: A comparison study

Cataract affects more than 20 million people worldwide and is the leading cause of vision loss. Currently, the phacoemulsification is the most used procedure to extract cataract and recover visual acuity. Optimal phacoemulsification energy is demanded for safety cataract removal. It is well established that the energy value is determined by the cataract hardness. In this study twenty porcine eyes were used as experimental samples. Cataract was induced by an ethanol:2-propanol:formalin solution. A 25 MHz focused transducer has been used to estimate the ultrasound velocity and attenuation. Statistical analysis was performed to compare the different used methodologies and to correlate the different ultrasound parameters with different stages of cataract formation (lens hardness).